1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display (LCD) and more particularly to the method for manufacturing the LCD which enables a display with a wide viewing angle.
The present application claims priority of Japanese Patent Application No. 2001-130421 filed on Apr. 26, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
For an LCD that can provide a wide viewing angle, in general, the display with a wide viewing angle is enabled by arranging a common electrode and a pixel electrode on a protecting film of a TFT (Thin Film Transistor) and by rotating a direction of a molecular axis of a liquid crystal molecule put in a liquid crystal layer in a hermetically sealed manner on a surface being parallel to a surface of an active matrix substrate. A typical example is an IPS (In-Plane Switching)-type LCD.
FIG. 20 shows schematic configurations of one pixel portion making up a conventional IPS-type LCD that can provide a wide viewing angle disclosed in Japanese Patent Application Laid-open No. Hei 10-186407. In the one pixel portion of the conventional IPS-type LCD disclosed above are provided a gate electrode 204, a drain line 206, a common electrode (ITO) (Indium Tin Oxide) 210, a common electrode 207, a pixel electrode (ITO) 211, a pixel electrode (drain layer) 213, and a TFT. In the IPS-type LCD, a display is performed by producing an electric field being substantially parallel to a surface of a substrate between the pixel electrode (ITO) 211 and the common electrode (ITO) 210 and by rotating a direction of a liquid crystal molecule within a face being parallel to the substrate surface according to the electric field. On the other hand, the TFT chiefly includes a source electrode 218, a drain electrode 215, and a semiconductor layer 219, or the like. There are provided two contact holes, one being a contact hole 217 for the common electrode (ITO) 210 and another being a contact hole 312 for the pixel electrode (ITO) 211.
FIGS. 21 to 26 are cross-sectional views showing processes 1-5 for manufacturing the conventional IPS-type LCD shown in FIG. 20. In each of FIGS. 21 to 26, a TFT element portion shows a cross-sectional view of the TFT of FIG. 20, taken along a line A—A′. A pixel portion is shown in a cross-sectional view of a part of the pixel portion of FIG. 20 taken along a line B-B′. A common electrode contact hole portion is shown in a cross-sectional view of the contact hole portion of FIG. 20 taken along a line C-C′. A gate terminal portion is shown in a cross-sectional view of a gate terminal, and a drain terminal portion is shown in a cross-sectional view of a drain terminal.
First, as shown in FIG. 21, a gate metal layer (not shown) is formed on a glass substrate by a sputtering method and the gate electrode 204 is formed using a first mask at a specified region on the gate metal layer in such a manner that a signal line for scanning (not shown) and the gate electrode 204 are integrally formed. Then, as shown in FIG. 22, an interlayer (gate) insulating film 223, an a−Si (amorphous silicon semiconductor) layer 238, and an n+a−Si (high concentration n-type amorphous silicon) layer 239 are sequentially formed by deposition on an entire surface of the glass substrate. By using a second mask, an island 235 is formed above the interlayer insulating film 223. Next, as shown in FIG. 23, a drain electrode metal layer is formed on the glass substrate by a sputtering method. Then, by using a third mask, a source electrode 218, a pixel electrode 213, a drain electrode 215, and a drain line 206 are formed so that the source electrode 218 and the pixel electrode 213 are integrally configured and the drain electrode 215 and the drain line 206 are integrally configured. A hollow, as shown in FIG. 23, is formed by performing dry (plasma) etching on a channel portion. At this point, since not only the n+a−Si layer 239 (FIG. 22) but also a−Si layer 238 (FIG. 22) is etched to some extent, a thickness of the deposited a−Si layer 238 is made larger. Then, as shown in FIG. 24, a passivation film 222 and an organic insulating film 221 are stacked on the glass substrate and an organic insulating film contact hole is formed in the organic insulating film 221 by using a fourth mask so that the organic insulating film contact hole passes through the organic insulating film 221 and reaches the passivation film 222 in order to provide a connection to the source electrode 218. Next, as shown in FIG. 25, portions of the passivation film 222 and the interlayer insulating film 223 being exposed are removed by an etching method using a fifth mask to form specified contact holes. Finally, as shown in FIG. 26, an ITO film 11 is formed by a sputtering method or the like so that its thickness is about 50 nm. Then, by using a sixth mask, unwanted portions of the ITO film 11 are removed by a wet etching method to provide a connection between the source electrode 218 and the pixel electrode 211. When a common electrode 210 is formed from the ITO film, sputtering of Cr (chromium) is performed on the passivation film 222 so that a thickness of the Cr film becomes 100 nm so that the common electrode 210 satisfies conditions described above. Then, an orientation film (not shown) is formed in a manner so as to cover all of them.
However, the conventional method for manufacturing the IPS-type LCD disclosed in Japanese Patent Application Laid-open No. Hei 10-186407 is problematic because the first to sixth masks are used, and the manufacturing process of the TFT is extended.
Moreover, when a known shortened process of manufacturing a TFT is employed in the case of manufacturing the IPS-type LCD, since a patterning process is performed on a semiconductor layer and an electrode in one photo resist process, a shape of the semiconductor layer and the electrode becomes the same and therefore a step of the TFT becomes larger, which makes it difficult to exert control on orientation of a liquid crystal. Thus, an increase in a black luminance and a so-called “floating black” are caused.
Furthermore, when the shortened processes for manufacturing the TFT are used, coverage by the passivation film becomes weak, which causes electrode materials (for source and drain electrodes) to penetrate into a liquid crystal from a coverage defective portion. Thus, a progressive display failure (dot-like stain or black stain) occurs.